1. Field of the Invention
The present invention relates generally to a permanent magnet generator, and more particularly to a permanent magnet generator that can be incorporated in a diskette designed to be used by inserting into a floppy disk drive, and when a memory, such as a magnetic card, is installed in the diskette, serves as a power source for the memory to write and read data in the memory.
2. Description of the Related Art
Medical information, such as personal medical checkup results, is stored in an IC card, from which medical institutions can retrieve such information for use in the treatment of a patient, and can store in the card the contents of his case records after some medical treatments. Plans are also now under way to use IC cards as electronic money. Under the plans, data on a customer""s bank account, password, and the balance of his account, if necessary, are stored in an IC card, by means of which payment is made on-line every time the card holder spends money.
It has been proposed that an enormous amount of video information handled by a digital camera be stored in a flash memory that has a capacity as large as several megabytes to 10 megabytes. A flash memory containing the video information taken by a digital camera can be connected to a personal computer for subsequent video processing. The use of a flash memory to record the video information taken by a digital camera may eliminate an additional external memory unit, such as MOs.
The widespread use of IC cards or flash memories, however, has been deterred by the need for special input/output (I/O) devices dedicated for such media. Since most commonly used I/O devices for personal computers are floppy disk drives, particularly 3.5xe2x80x3 floppy disk drives, the use of 3.5xe2x80x3 floppy disks as an I/O device for IC cards and flash memories could spur their proliferation. In fact, methods for writing and reading data into and from an IC card or flash memory are being studied, and adapters that can be inserted or incorporated in 3.5xe2x80x3 floppy disk drives have already been proposed. A conventional type of 3.5xe2x80x3 floppy disk drive has a magnetic head to read and write information from and into a 3.5xe2x80x3 diskette, and a drive shaft to cause the diskette to rotate at 300 rpm, but it has no power feeding terminals. In diskette-shaped adapters, a button battery is incorporated to power the built-in CPU. A battery, which depletes as it is used, has to be replaced with a new one every four to five months at the longest.
Introduction of a 3.5xe2x80x3 floppy disk in which a generator is incorporated and driven by the rotation of the drive shaft of a 3.5xe2x80x3 floppy disk drive would prove very useful, giving momentum to the proliferation of IC cards and similar media. In fact, the concept of incorporating a generator in a 3.5xe2x80x3 diskette has already been proposed in U.S. Pat. No. 5,159,182 SMART DATA STORAGE DEVICE, issued Oct. 27, 1992 to Raymund H. Eisele and Tokuhyo Hei-7(1995)-500238, a published Japanese translation of PCT international publication for patent application.
U.S. Pat. No. 5,159,182 discloses that a generator is incorporated in a 3.5xe2x80x3 diskette, and that the generator has a rotor, a stator and a regulator, but its detailed construction is not disclosed. Tokuhyo Hei-7(1995)-500238 discloses a generator incorporated in a 3.5xe2x80x3 diskette having a permanent magnet that rotates with a hub, which is caused to rotate by the drive shaft of a floppy disc drive. This permanent magnet is of a cylindrical shape, magnetized in the axial direction so that multiple magnetic poles are provided on the both end faces of the cylinder. The magnetic poles of a stator yoke are disposed in such a manner as to sandwich the cylindrical permanent magnet, and a stator coil is provided between the stator yokes on both sides of the cylindrical permanent magnet. Another example is also disclosed in which magnetic poles are provided on the circumferential surface of the cylindrical permanent magnet. In this example, the magnetic poles of the stator yoke are of a claw pole shape.
Now, let us consider a permanent magnet generator of a size that can be incorporated in a 3.5xe2x80x3 floppy disk, as disclosed in Tokuhyo Hei-7(1995)500238, where the cylindrical permanent magnet is magnetized in the direction of the rotating shaft of the rotating permanent magnet in such a manner that multiple magnetic poles are provided on the both end faces of the cylinder. In this case, stator magnetic poles are disposed on both sides of the cylinder end face with small magnetic gaps. Since the allowable thickness of a generator in a diskette is 2.0 to 2.5 mm, the permanent magnet is allowed to have a thickness of only 0.5 to 0.8 mm at most. Even when a material having a large coercive force is used for a magnet with such a short distance between magnetic poles, only a small magnetomotive force could be expected. Even if magnetomotive force is increased by increasing the thickness of the magnet, the allowable thickness of the stator magnetic poles is reduced, making it difficult to pass a sufficient amount of magnetic flux in them.
In a permanent magnet generator where magnetic poles are provided on the circumferential surface of the cylindrical permanent magnet and the claw pole type stator yoke is provided, as disclosed in Tokuhyo Hei-7(1995)-500238, the end yokes of both claw pole type magnetic poles are provided facing each other within the thickness of 2.0 to 2.5 mm allowed for the generator, and a stator winding is provided between the end yokes. Since a sufficient number of winding turns cannot be provided within the thickness of no more than 1 mm allowed for the stator winding, a generator having a low output voltage would inevitably result.
In order to realize a generator having as high an output as possible and the lowest possible distortion, it is necessary to dispose rotor magnetic poles on the circumferential surface of the cylindrical permanent magnet at equal angular intervals, and make the number of magnetic poles of the stator yokes equal to the number of magnetic poles of the rotor permanent magnet, so that the stator magnetic poles can face the permanent magnet magnetic poles.
In order to implement a diskette which serves as an information I/O device in conjunction with a memory card having magnetic stripes, such as an IC card, a space for housing a memory card must be provided in the diskette. The typical size of a standard memory card is 85 mm in length, 54 mm in width, and 0.8 mm in thickness. Since the thickness given above ignores the embossed part for raised letters of the memory card, its actual thickness is a little bit thicker. To provide a space for a memory card and a permanent magnet type generator in a 3.5xe2x80x3 diskette having a thickness of 3.5 mm and two 0.2 mm-thick covers on both sides, the thickness of the generator must be not more than 2.0 mm, allowing for the thickness of the memory card of 0.8 mm and some clearance for loading and unloading the card.
One of the present assignees has already filed a U.S. patent application for a diskette having a permanent magnet type generator, Ser. No. 09/369,420, filed Aug. 6, 1999. The diskette according to the patent application is shown in FIG. 19. A diskette 9 shown in the figure incorporates a permanent magnet generator 90 around a hub 911 disposed at the center thereof in such a manner that a ring-shaped permanent magnet 912 having magnetic poles on the outer circumferential surface thereof can be rotated together with the hub. A generator stator 92 is provided inside the diskette on the outer periphery of a permanent magnet 912 of a rotor 91, with a magnetic gap between the magnetic poles on the outer circumferential surface of the permanent magnet 912. The diskette 9, which is designed to be used as an I/O device for IC card or memory card, has a space 95 for accommodating a memory card, and a card contact terminal 96 used for exchanging information with the memory card. An I/O terminal 97 for exchanging information between the diskette and a magnetic head of a floppy disk drive is provided at an opening 93 provided for allowing the magnetic head to access the diskette. A CPU 98 is provided as necessary to process information between the I/O terminal 97 and the card contact terminal 96. The permanent magnet generator 90 is used as a power source for driving the CPU 98 and the card contact terminal 96. As a drive power, the output of the generator is usually fed via a stabilized power supply circuit 99.
The permanent magnet generator disclosed in U.S. patent application Ser. No. 09/369,420 has a permanent magnet rotor with magnetic poles on the outer circumferential surface of a ring-shaped permanent magnet, stator magnetic poles arranged on the circumferential inside surface at such positions that the stator magnetic poles can face the rotor magnetic poles, and stator magnetic pole teeth extending outward from each of the stator magnetic poles. To increase the output of the permanent magnet generator, a permanent magnet having the highest possible coercive force and residual magnetic flux density, or more desirably a sintered anisotropic NdFeB magnet, is used. Coils wound on stator magnetic pole teeth should have as many as 6000 turns in total.
The rotation of the rotor, however, relies solely on the rotating force of the floppy disk drive, which is typically as small as 300 rpm. This limits the output of the generator to 20 mW or so at most.
The use of a sintered NdFeB magnet having good magnetic characteristics to improve the output, on the other hand, would tend to increase cogging torque because the magnetic flux density around the magnet rotor using this magnet almost invariably becomes a square wave, resulting in a steep magnetic flux density distribution between the magnetic poles. To ensure the smooth rotation of the rotor of a permanent magnet generator in a floppy disk drive, it is necessary to limit the cogging torque of the rotor to not more than 2.5 mNm at most. To this end, various attempts, including providing enclosed slots between the stator magnetic poles, have been made to reduce cogging torque. The enclosed slot type stator, however, has often further reduced the output because part of the magnetic flux from the magnet rotor is short-circuited between the stator magnetic poles.
As described earlier, attempts have been made to increase the number of turns of the stator coil to cope with the output, but fine windings have had to be used to provide a large amount of windings in a limited space of the diskette, resulting in an increase in the internal resistance of the generator. Furthermore, the length of the magnetic pole teeth has had to be increase to allow a large amount of windings to be wound on the stator magnetic pole teeth. This has not only increased magnetic resistance but also required a larger space within a limited space in the diskette.
All this has led to an increase in the cost of a permanent magnet generator incorporated in a diskette.
It is therefore an object of the present invention to provide a diskette incorporating a permanent magnet generator that can reduce or eliminate the aforementioned shortcomings and ensure a high generating output.
It is another object of the present invention to provide a diskette incorporating a permanent magnet generator whose generating output is increased by reducing cogging torque.
It is a further object of the present invention to provide a diskette in which the thickness of a generator or a magnet used therein can be increased by preventing a space for a memory card from overlapping with a permanent magnet generator.
It is a still further object of the present invention to provide a diskette incorporating a permanent magnet generator that can be manufactured at low cost.
To achieve these objectives, the diskette incorporating a permanent magnet according to the present invention comprises
a diskette case having a magnetic disk shape, and
a hub provided therein and driven by an external driving mechanism, and
a permanent magnet generator provided inside the diskette case and having a rotor that is caused to rotate by the hub;
the permanent magnet generator comprising
a rotor having a rotatable (preferably, ring-shaped) permanent magnet having a plurality of magnetic poles arranged on the circumference thereof which magnetic poles have alternately different polarities in the circumferential direction, and
a stator having a plurality of stator magnetic pole teeth, the plurality of stator magnetic pole teeth each having a stator magnetic pole at an end thereof disposed at such a position as to be able to face one of the rotor magnetic poles via a magnetic gap, extending outward from the stator magnetic pole and having a stator coil wound thereon;
the rotor and the stator formed into a flat disc shape as a whole,
in which a rotation transmitting mechanism for connecting the rotor of the permanent magnet generator to the hub is provided inside the diskette case; the rotation transmitting mechanism being a speed increasing mechanism.
In the diskette incorporating a permanent magnet generator according to the present invention, the rotation transmitting mechanism should preferably be a speed increasing mechanism capable of increasing speed twofold to tenfold. The rotating axis of the hub can be arranged coaxially or offset with the rotating axis of the rotor. The rotation transmitting mechanism may be of an endless belt type, or a gear type, or a rubber roller type. When the rotating axis of the hub is arranged coaxially with the rotating axis of the rotor, with the rotation transmitting mechanism being of a coaxial type, the coaxial rotation transmitting mechanism should preferably be of a planetary type.
The diskette incorporating a permanent magnet generator according to the present invention may comprise:
a diskette case having magnetic disk shape, and
a hub provided therein and driven by an external driving mechanism, and
a permanent magnet generator provided inside the diskette case and having a rotor that is caused to rotate by the hub;
the permanent magnet generator comprising
a rotor having a rotatable (preferably, ring-shaped) permanent magnet having a plurality of magnetic poles arranged on the circumference thereof which magnetic poles have alternately different polarities in the circumferential direction, and
a stator having a plurality of stator magnetic pole teeth, the plurality of stator magnetic pole teeth each having a stator magnetic pole at an end thereof disposed at such a position as to be able to face one of the rotor magnetic poles via a magnetic gap, extending outward from the stator magnetic pole and having a stator coil wound thereon;
the rotor and the stator constructed into a flat disc as a whole,
in which a rotation transmitting mechanism for connecting the rotor of the permanent magnet generator to the hub is provided inside the diskette case, and the rotating axis of the hub is arranged offset with the rotating axis of the rotor. In such a case, a space for accommodating a memory card is provided in the diskette case; the space should preferably be not overlapped with the permanent magnet generator while lying within a plane inside the diskette case.
In the diskette incorporating a permanent magnet generator according to the present invention, the gap magnetic flux density distribution of the permanent magnet generator should preferably be a sinusoidal curve. In such a case, the (ring-shaped) permanent magnet should preferably be a bonded magnet.
In the diskette incorporating a permanent magnet according to the present invention, it is desirable that certain stator magnetic poles among the stator magnetic poles of the generator be disposed at such locations as to be able to face the rotor magnetic poles, and that the remaining stator magnetic poles be disposed at locations about 90 degrees, in terms of electrical angle, shifted from the aforementioned certain number of stator magnetic poles to reduce cogging torque. It is also desirable that the number of certain stator magnetic poles disposed at such locations as to be able to face the rotor magnetic poles be about half of the total number of the stator magnetic poles. It is also desirable that certain stator magnetic pole teeth extending outward of the rotor from each of the certain number of stator magnetic poles and having stator coils wound thereon be connected to each other by a back yoke made of soft magnetic material at the outer side edges, and the stator magnetic pole teeth extending outward of the rotor from each of the remaining stator magnetic poles and having stator coils wound thereon be connected to each other by another back yoke made of soft magnetic material at the outer side edges.
The stator used in the present invention should preferably have a plurality of auxiliary magnetic poles at such locations as to be able to face the rotor magnetic poles via magnetic gaps; each of the auxiliary magnetic poles preferably not having stator coils and being connected to each other by back yokes made of soft magnetic material to further reduce cogging torque. It is also desirable that the pitch of the auxiliary magnetic poles be xc2xd of the pitch of the rotor magnetic poles. The number of the auxiliary magnetic poles should preferably be equal to the number of the stator magnetic poles at most.
Using the diskette of the present invention having the aforementioned construction, the generating output of a permanent magnet generator is increased more than twofold and the revolution of the generator rotor is increased about sixfold via a rotation transmitting mechanism. Thus, the output of the generator is increased about six times as high as the conventional type of generator. This generator in which cogging torque is reduced can achieve a large generating output and ensure smooth generator rotation because its rotating torque does not exceed the allowable maximum torque of the floppy disk drive even when the rotation of the rotor is increased sixfold by the rotation transmitting mechanism.